Mounting an airbag device configured to absorb an impact applied on an occupant by inflating and deploying an airbag in a cabin in case of collision or sudden deceleration on a vehicle such as an automotive vehicle is becoming popular. As such an airbag device, various types such as a driver airbag device mounted in the interior of a steering, a passenger airbag device mounted in the interior of an instrument panel, side airbag devices mounted in the interiors of vehicle side surface portions or in the interiors of seats, curtain airbag devices mounted in the interiors of upper portions of doors, knee airbag devices corresponding to knees of the occupants, a pedestrian airbag device mounted in the interior of a portion under a hood, and so on are developed and employed. Recently, a motorcycle airbag is also developed.
Such an airbag device is generally included a gas generator configured to generate gas under predetermined conditions, an airbag configured to be inflated and deployed by being connected to the gas generator, and a retainer configured to store an airbag. Various types of shapes and configurations of the airbag are applied according to the places to be installed and required functions or the like.
Here, airbags described in U.S. Pat. No. 6,086,092 and Japanese Unexamined Patent Application Publication No. 2006-151350 are configured to have a small chamber (first chamber, inner bag, etc.) in the airbag, and allow gas from an inflator to flow into the airbag step by step. In this configuration, a center portion of the airbag can be inflated and deployed prior to an outer peripheral portion of the airbag, the airbag can be projected quickly, a space with respect to the occupant can be filled quickly, and a gas flow into the outer peripheral portion can be accelerated because the length in the direction of thickness is restrained. The small chamber is referred to as an inner chamber, hereinafter.
However, when providing the inner chamber in the airbag, the amount of base cloth to be used for the entire airbag is increased inevitably, and the size of a package when the airbag is folded is also increased. Therefore, there arise problems that the cost of the airbag is increased, the retainer cannot accommodate the airbag, or upsizing of the retainer is required or the like. In contrast, if the amount of the base cloth of the inner chamber is reduced too much, there arises a problem that it does not function as the inner chamber. There is also a problem that a seamed portion formed when the inner chamber is connected in the airbag has high rigidity and hence resists easy folding, and hence the size of the package when the airbag is folded is likely to be increased.